Earth Equity News

Getting to 350. By Richard Monastersky, Nature, April 29, 2009. "In 2007, environmental writer Bill McKibben approached climate scientist James Hansen and asked him what atmospheric concentration of carbon dioxide could be considered safe. Hansen's reaction: 'I don't know, but I'll get back to you.' After he had mulled it over, Hansen started to suspect that he and many other scientists had underestimated the long-term effects of greenhouse warming. Atmospheric concentration of CO2 at the time was rising past 382 parts per million (p.p.m.), a full 100 ticks above its pre-industrial level. Most researchers, including Hansen, had been focusing on 450 p.p.m. as a target that would avoid, in the resonant and legally binding formulation of the United Nations Framework Convention on Climate Change, 'dangerous climate change'... He came back to McKibben with not 450 but 350. In 2008, he published a paper spelling out his rationale for that target. The difference between 350 and 450 is not just one of degree. It's one of direction."